Commercial article printing typically occurs during the production of the article. For example, ball skins are printed with patterns or logos prior to the ball being completed and inflated. Consequently, a non-production establishment, such as a distribution site or retail store, for example, in a region in which potential product customers support multiple professional or collegiate teams, needs to keep an inventory of products bearing the logos of various teams popular in the area. Ordering the correct number of products for each different logo to maintain the inventory can be problematic.
One way to address these issues in non-production outlets is to keep unprinted versions of the products, and print the patterns or logos on them at the distribution site or retail store. Printers known as direct-to-object (DTO) printers have been developed for printing individual objects. Some of these printers use UV curable inks to form ink images on the objects. UV curable inks require a UV radiation source that directs UV light onto the inks on the object surface. This light cures the inks and helps eliminate vapors that otherwise emanate from the inks. Some of these vapors can be noxious to humans.
UV radiating light emitting diodes (LEDs) are one efficient form of UV radiation sources. These semiconductor devices generate light in the UV range of the light spectrum in response to a DC voltage being applied to the semiconductor junction in the device. Typically, these UV LEDs are arranged in an array of LEDs that extend in the cross-process direction, which is perpendicular to the path of movement for the holder and the object passing by one or more printheads for ink printing. As used in this document, “process direction” refers the direction of movement of an object past the printheads in a printer and “cross-process direction” refers to an axis that is perpendicular to the process direction in a plane parallel to the plane in which the holder of the object is moving. Over the operational life of the UV LEDs, some of the LEDs begin producing radiation at lower levels until they no longer emit an UV light with an effective intensity for curing UV inks. Detecting this demise of UV LEDs in a printer prior to them becoming completely ineffective for UV ink curing would be beneficial.